Coarctation of the aorta (CoA) is a relatively common defect that accounts for 5-8% of all congenital heart defects. Coarctation of the aorta may occur as an isolated defect or in association with various other lesions, most commonly bicuspid aortic valve and ventricular septal defect (VSD). The diagnosis of coarctation of the aorta may be missed unless an index of suspicion is maintained, and diagnosis is often delayed until the patient develops congestive heart failure (CHF), which is common in infants, or hypertension, which is common in older children. This article discusses the pathology, pathophysiology, clinical features, noninvasive and invasive evaluation, and therapy in patients with coarctation of the aorta.
Coarctation of the aorta may be defined as a constricted aortic segment that comprises localized medial thickening, with some infolding of the medial and superimposed neointimal tissue.  The localized constriction may form a shelflike structure with an eccentric opening or may be a membranous curtainlike structure with a central or eccentric opening. The coarctation may be discrete, or a long segment of the aorta may be narrowed; the former is more common.
In the past, coarctation of the aorta has been described as preductal (or infantile) type or postductal (or adult) type, depending on whether the coarctation segment is proximal or distal to the ductus arteriosus, respectively. However, a closer examination of the anatomy suggests that all coarctations are juxtaductal.
The classic coarctation of the aorta is located in the thoracic aorta distal to the origin of the left subclavian artery at about the level of the ductal structure. However, rarely, a coarcted segment is present in the lower thoracic or abdominal aorta. In such instances, the coarcted segment may be long and fusiform with irregular lumen; many consider these to be inflammatory or autoimmune in origin, and they may be variants of Takayasu arteritis.
Dilatation of the descending aorta immediately distal to the coarctation segment (poststenotic dilatation) is usually present. A jet lesion on the wall of the aorta distal to the coarctation site may also be present. Varying degrees of hypoplasia of the isthmus of the aorta (the portion of the aorta between the origin of the left subclavian artery and ductus arteriosus) are present in most patients with thoracic coarctation; this hypoplasia may be significant in symptomatic coarctation of the neonate and infant; in children and adults, the isthmus may have only mild narrowing. The transverse aortic arch (the arch between the origin of the right innominate artery and the left subclavian artery) is also hypoplastic in symptomatic neonates and infants. Collateral vessels that connect arteries from the upper part of the body to the vessels below the level of coarctation may be seen; these may be present as early as a few weeks to a few months of life.
The most commonly associated clinically significant defects include patent ductus arteriosus, VSD, and aortic stenosis. The earlier the infant presents, the more likely a significant associated defect is present. Bicuspid aortic valve may be seen in nearly two thirds of infants with coarctation of the aorta, whereas only 30% of those who present in childhood have such an anomaly.
Mitral valve anomalies, although less common than those of the aortic valve, are also associated with coarctation of the aorta. Sometimes, coarctation of the aorta is a complicating feature of a more complex cyanotic heart defect, such as transposition of the great arteries, Taussig-Bing anomaly, double-inlet left ventricle, tricuspid atresia with transposition of the great arteries, and hypoplastic left heart syndrome.
Aortic coarctation is extremely rare in patients with severe right ventricular outflow tract obstructions such as tetralogy of Fallot and pulmonary atresia with intact ventricular septum. Some patients with coarctation of the aorta may have cerebral aneurysms, predisposing them to cerebrovascular accidents with severe hypertension later in life. Coarctation of the aorta is the most common cardiac defect associated with Turner syndrome.
The exact mechanism by which aortic coarctation is produced is not clearly understood. The most commonly invoked hypotheses include hemodynamic and ectopic ductal tissue theories. In the hemodynamic theory, an abnormal preductal flow or abnormal angle between the ductus and aorta that increases right-to-left ductal flow and decreases isthmic flow potentiates development of coarctation. Postnatal spontaneous closure of the ductus arteriosus completes the development of aortic obstruction. [2, 3]
A high incidence of coarctation of the aorta in patients with congenital heart defects with decreased antegrade aortic flow in utero and virtual absence of CoA in patients with right heart obstructions lends credence to the hemodynamic theory. Abnormal extension of ductal tissue into the aorta (ectopic ductal tissue). [4, 5] has been postulated to create the coarctation shelf and, with ductal closure, development of aortic obstruction. This theory, however, does not explain the variable degrees of isthmus and aortic arch hypoplasia associated with coarctation of the aorta.
Coarctation of the aorta imposes significant afterload on the left ventricle (LV), which results in increased wall stress and compensatory ventricular hypertrophy.
The afterload may be imposed acutely, as occurs following closure of the ductus arteriosus in neonates with severe coarctation. These infants may rapidly develop CHF and shock. Rapid constriction of the ductus arteriosus, producing sudden severe aortic obstruction, seems to be the most likely explanation. As the ductus (aortic end) constricts, the left ventricular afterload rapidly increases, with a resultant increase in left ventricular pressures (systolic and diastolic). This causes elevation of the left atrial pressure, which may open the foramen ovale, causing left-to-right shunt and dilatation of the right atrium and right ventricle. If the foramen ovale does not open, pulmonary venous pressures and pulmonary artery pressures increase, and right ventricular dilatation develops.
Cardiomegaly revealed by chest roentgenography and right ventricular hypertrophy seen on ECG and echocardiography are related to the indirect effects of rapid development of severe aortic obstruction.
LV afterload may also gradually increase, allowing children with less severe coarctation to develop arterial collateral vessels that partially bypass the aortic obstruction. These children may be asymptomatic until hypertension is detected or another complication develops.
The mechanism for development of hypertension is not clearly understood; mechanical obstruction and renin-angiotensin–mediated humoral mechanisms have been postulated.
The mechanical obstruction theory explains the increased blood pressure by postulating that a higher blood pressure is required to maintain flow through the coarcted segment and collateral vessels. The stroke volume, ejected into the limited aortic receptacle, produces a higher pressure proximal to coarctation. However, this theory does not explain the following:
The lack of relationship between the degree of elevation of blood pressure and the magnitude of obstruction
The increased peripheral vascular resistance distal to the site of obstruction
The delayed or lack of reduction of blood pressure immediately following relief of obstruction
The humoral theory postulates activation of the renin-angiotensin system secondary to reduction of renal blood flow and appears to explain most of the clinical features. [6, 7, 8] However, measurement of plasma renin activity in both animal models and human subjects did not show consistently elevated plasma renin levels in the early studies. The reasons for the inability to demonstrate elevation of renin levels may be related to inadequate measurement of salt intake, posture, extracellular fluid volume, and sympathetic influences on renin release. More recent studies demonstrated abnormalities in renin-angiotensin-aldosterone systems.  In addition, activation of central sympathetic nervous system may also be responsible for hypertension of aortic coarctation. 
Associated anomalies greatly influence pathophysiology.  VSD is frequently present, and coarctation exacerbates the associated left-to-right shunt. Other levels of left heart obstruction (aortic stenosis, subaortic stenosis) may be present and may add to LV afterload.
Numerous neurohumoral changes occur with CHF.  Sympathetic nervous system activation occurs, resulting in increases in heart rate and blood pressure (BP). The renin-angiotensin system is activated in patients with CHF, particularly in coarctation of the aorta, in which lower-body BP and renal perfusion may be reduced. Activation of the renin-angiotensin system results in vasoconstriction, cell hypertrophy, and the release of aldosterone. The role of the renin-angiotensin system in CHF and the use of drugs to modulate this system are an intense area of research. Unlike most cases of CHF, coarctation of the aorta is more complex because precoarctation and postcoarctation hemodynamics are quite different.
Drugs typically used to treat patients with CHF, such as angiotensin-converting enzyme (ACE) inhibitors and, more recently, angiotensin II antagonists, may have adverse effects in patients with coarctation of the aorta. Attempts to achieve a normal precoarctation BP with these drugs may result in inadequate lower-body perfusion and may precipitate renal failure.
Vasopressin is also increased in heart failure, although its major stimulus for release is angiotensin II. Vasopressin affects free water retention and may result in hyponatremia. The vasoconstrictive properties of vasopressin may further elevate BP in coarctation.
Other substances, such as human brain natriuretic peptide (BNP), an endothelin, may be activated by CHF, although their specific role in coarctation has not been studied.
An additional cause of coarctation of the aorta is trauma that results in aortic dissection. Compromise of the true lumen of the aorta can result in the clinical picture of coarctation with reduced lower-extremity pulses. Urgent intervention is required in this circumstance.
Coarctation of the aorta is a lifelong disease with a guarded prognosis. Relief of obstruction, control of hypertension, follow-up monitoring for recurrent obstruction, and follow-up care of associated anomalies are imperative.
Continue subacute bacterial endocarditis prophylaxis indefinitely, even in the absence of associated abnormalities. Patients without residual obstruction who are normotensive both at rest and with exercise should lead normally active lives without restriction. They should be able to obtain health and life insurance.
Patients with persistent hypertension, untreated residual obstruction, or other complications have a variable prognosis related to the severity of these problems.
Data regarding long-term follow-up are limited. Available studies indicate that significant mortality rates are found at long-term follow-up after surgical correction of aortic coarctation.  The survival curve, while not approaching that in the healthy population, is significantly improved compared with Campbell's natural history data.  Death appears to be secondary to recoarctation repair, aneurysms at site of coarctation repair or at a remote site, congestive heart failure, bacterial endocarditis, and hypertension. Attempts to define factors that affect long-term survival have been made; age at operation and degree and duration of hypertension prior to surgery appear to affect the long-term survival.
A study by Oliver et al indicated that in young adults who underwent aortic coarctation repair in childhood, the greatest risk factor for heart failure or cardiovascular death is pulmonary hypertension related to restrictive LV physiology. The study involved 159 adults who underwent aortic coarctation repair at mean age 4.1 years. The investigators found that those individuals with a pulmonary artery systolic pressure of over 40 mm Hg were at the greatest risk of death or of being admitted to the hospital for heart failure. Using logistic regression analysis, they also found that pulmonary hypertension in the adults studied was predicted primarily by restrictive LV physiology. 
The study did not find heart failure or death to be statistically associated with recoarctation, systemic hypertension, intracardiac lesions, or aortic aneurysm or with treatment with beta blockers or ACE inhibitors/angiotensin receptor blockers. 
Past autopsy studies suggest that the mortality rate in patients in whom coarctation of the aorta is not surgically repaired is 90% by age 50 years, with a mean age of 35 years.  In the current era, coarctation of the aorta mortality is often determined by patient age, patient size, and associated major cardiovascular anomalies.
Associated problems that may contribute to death or morbidity include hypertension, intracranial hemorrhage, aortic rupture or dissection, endocarditis, and CHF.
Coarctation of the aorta is a lifelong disease with complications that may not be evident until many years following an initial and apparently successful repair.
Recurrence of coarctation is associated with patient size, age at surgery, and associated transverse arch or isthmic hypoplasia. Ductal tissue in the wall of the aorta may involute and contribute to recurrence, as might scarring at the repair site. Some surgeons believe that the use of interrupted sutures in the anterior portion of the anastomotic suture line improves aortic growth and reduces the risk of recurrence. Sometimes, the surgical repair site is unobstructed, yet obstruction develops at the transverse arch or isthmus because of the failure of these areas to grow proportionally to the rest of the arch. Such obstruction may not be detected for many years after initial repair.
Some patients who have undergone initial repair with left subclavian flap aortoplasty may have a tortuosity at the repair site that does not result in obstruction until rapid growth in adolescence.
Aneurysm of the aorta can occur in unrepaired coarctation of the aorta and has been described in patients with Turner syndrome and coarctation of the aorta. In addition, endocarditis can result in aortic arch aneurysm (mycotic aneurysm), usually distal to the site of obstruction.
Patch repair of coarctation of the aorta results in an increased incidence of aortic aneurysm (usually opposite the site of the patch), particularly if the shelf of coarcted tissue is excised. Patients with aortic aneurysm can be entirely asymptomatic. Hoarseness that results from stretching of the recurrent laryngeal nerve associated with aortic aneurysm has been described. Chest radiographs are unlikely to reveal the aortic aneurysm, but MRI is more useful in delineating the size and extent of aneurysms.
Hypertension may persist, even after successful repair of coarctation of the aorta, and usually relates to the duration and severity of preoperative hypertension. This is probably related to alterations in the renin-angiotensin system and baroreceptors. As with other forms of uncontrolled hypertension, patients may be at risk for premature atherosclerosis, ventricular dysfunction, and rupture of cerebral aneurysms.
Berry aneurysms of the circle of Willis or other vessels are believed to occur in as many as 10% of patients with coarctation of the aorta and may be multiple. Aneurysm size tends to increase with age, as does the risk of rupture. Uncontrolled hypertension promotes the growth of the aneurysms and increases risk of rupture. Most patients are asymptomatic until rupture occurs, although some aneurysms may leak prior to rupture, resulting in warning symptoms of headache, photophobia, weakness, or other symptoms. Rupture of a cerebral aneurysm is associated with high mortality rates and should prompt repair of both the aneurysm and coarctation.
Although rare, paraplegia can occur from spinal cord ischemia, resulting from a compromised blood supply to the anterior spinal artery. [20, 21] Risk of paralysis is increased with reduced arterial collateral vessels, prolonged aortic cross-clamping time, and intraoperative sacrifice of intercostal arteries, as well as other factors.
Paralysis is uncommon in the presence of a well-developed arterial collateral supply, emphasizing the importance of assessing collateral arterial flow prior to surgical intervention. Methods to prevent cord ischemia include hypothermia, use of cardiopulmonary bypass, or insertion of a bypass graft (Gott shunt) with partial aortic clamping.
Cardiomyopathy is usually present in infants with critical coarctation, especially if additional levels of left heart obstruction, such as aortic stenosis or subaortic stenosis, are present. Some patients may have changes of endocardial fibroelastosis that result in chronic dilated cardiomyopathy, requiring medical management or, in rare cases, cardiac transplantation. Hypertrophic cardiomyopathic changes also may occur, predisposing the patient to subendocardial ischemia, arrhythmias, or congestive heart failure (CHF) related to diastolic dysfunction.
Extensive dissection at surgery may result in disruption of the thoracic duct, leading to chylothorax. Chylothorax is recognized when feedings are instituted postoperatively. Persistent chylous pleural effusions may necessitate long-term chest tube drainage. Some patients respond to dietary therapy with medium-chain triglyceride diet, fat restriction, and/or total parental nutrition. Patients with refractory chylothorax may require pleurodesis or thoracic duct ligation.
Restoring pulsatile blood flow to the mesenteric arteries may result in mesenteric arteritis, in which the arteries become distended and may rupture. Reflex arteriolar vasoconstriction occurs as part of autoregulation of blood flow and can result in ischemia.
Clinical manifestations may range from mild abdominal discomfort to an acute abdomen with severe abdominal distention, vomiting, ileus, and progression to intestinal wall hemorrhage or perforation. This syndrome may be related to early return to feeding after coarctation repair. Thus, feedings are usually delayed for 48 hours after surgery, and nasogastric tube decompression is continued until feedings are begun slowly and advanced as tolerated. Patients with severe postcoarctectomy syndrome may require exploratory laparotomy for treatment of bowel necrosis or perforation.
Careful monitoring and good control of BP in the postoperative period may reduce the risk of postcoarctectomy syndrome.
Valvar aortic stenosis, membranous subaortic stenosis, and mitral valve stenosis
These may develop during the follow-up period; if these are significant, transcatheter or surgical relief of the obstruction may become necessary.
No definitive racial differences have been documented in coarctation of the aorta, although some authors have suggested that coarctation of the aorta is less common in Asians. 
The male-to-female ratio is 2:1, although this ratio is not valid in abdominal coarctation of the aorta, in which this rare lesion predominantly affects females. The ratio of abdominal-to-thoracic coarctation is approximately 1:1000. The male preponderance observed in older patients is not seen in infants with coarctation of the aorta.
Generally, patients with coarctation of the aorta present early in life with CHF or later in life with hypertension. Studies continue to document that coarctation of the aorta is often missed in the first year of life, [25, 26] and the median age of referral to a pediatric cardiologist in one study was 5 years. Among 2192 patients reported to the Pediatric Cardiac Care Consortium from 1985-1993, 1337 were infants, 824 were children, and 31 were adults. 
Coarctation of the aorta is a common defect and occurs in 6-8% of patients with congenital heart disease. [13, 14] However, coarctation may be found more frequently in infants who present with symptoms prior to age one year. 
The prevalence of coarctation of the aorta appears to be lower (< 2%) in Asian countries than in European and North American countries. 
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